urm ive just recently joined vodafone contract (never been on contract before) and on the Vodafone site under 'My Vodafone' you need to log in providing you have registed with the site which you need to do and it is quite helpfull too. Log-In and then click 'My Account' on the left and a menu will drop down and just select 'Change your price plan & Extra Packs'
KIIS102